One type of hydraulic rotary device used to provide torque resistance device is disclosed in U.S. Pat. No. 4,941,554. It includes a rotor and a stator disposed in a hermetically sealed cylindrical chamber. The cylindrical chamber, which is normally filled with hydraulic fluid, is divided into two pressure chambers by the rotor and the stator. The two pressure chambers are interconnected externally of the housing by a bypass conduit which carries hydraulic fluid from one pressure chamber to the other as the rotor is rotated. A manually adjustable flow restrictor is located in the bypass conduit, and the setting of the restrictor determines the force required to move the hydraulic liquid from one side of the stator to the other and, consequently, the torque required to rotate the rotor.
It would be desirable to permit a computer or other device to control the setting of the restrictor so as, for example, automatically to adjust the torque required to rotate the rotor in response to the energy being expended to rotate the rotor. Such a device would be especially desirable in an exercise machine to permit the presetting of an exercise regimen, and to permit automatic adjustment of the regimen in response to the work being done by the person doing an exercise.
It would also be desirable to control the speed of a rotary actuator by controlling the flow resistance of a flow restrictor connected in a bypass conduit between the pressure chambers in a rotary actuator. In this manner a computer can be used to control the setting of the flow restrictor and could be programmed to vary the speed and range of movement of the oscillating output shaft of a rotary actuator.